TH2F *h2;
TH1D * projh2X;
TH1D * projh2Y;
TPad *right_pad, *top_pad;

%%cpp -d
void ZoomExec()
{
   int xfirst = h2->GetXaxis()->GetFirst();
   int xlast = h2->GetXaxis()->GetLast();
   double xmin = h2->GetXaxis()->GetBinLowEdge(xfirst);
   double xmax = h2->GetXaxis()->GetBinUpEdge(xlast);
   projh2X->GetXaxis()->SetRangeUser(xmin, xmax);
   top_pad->Modified();

   int yfirst = h2->GetYaxis()->GetFirst();
   int ylast = h2->GetYaxis()->GetLast();
   double ymin = h2->GetYaxis()->GetBinLowEdge(yfirst);
   double ymax = h2->GetYaxis()->GetBinUpEdge(ylast);
   projh2Y->GetXaxis()->SetRangeUser(ymin, ymax);
   right_pad->Modified();
}

auto c1 = new TCanvas("c1", "c1",900,900);
gStyle->SetOptStat(0);

TPad *center_pad = new TPad("center_pad", "center_pad",0.0,0.0,0.6,0.6);
center_pad->Draw();

right_pad = new TPad("right_pad", "right_pad",0.55,0.0,1.0,0.6);
right_pad->Draw();

top_pad = new TPad("top_pad", "top_pad",0.0,0.55,0.6,1.0);
top_pad->Draw();

h2 = new TH2F("h2","",40,-4,4,40,-20,20);
Float_t px, py;
for (Int_t i = 0; i < 25000; i++) {
   gRandom->Rannor(px,py);
   h2->Fill(px,5*py);
}
projh2X = h2->ProjectionX();
projh2Y = h2->ProjectionY();

center_pad->cd();
gStyle->SetPalette(1);
h2->Draw("COL");

top_pad->cd();
projh2X->SetFillColor(kBlue+1);
projh2X->Draw("bar");

right_pad->cd();
projh2Y->SetFillColor(kBlue-2);
projh2Y->Draw("hbar");

c1->cd();
TLatex t;
t.SetTextFont(42);
t.SetTextSize(0.02);
t.DrawLatex(0.6,0.88,"This example demonstrates how to display");
t.DrawLatex(0.6,0.85,"a histogram and its two projections.");

auto ex = new TExec("zoom","ZoomExec()");
h2->GetListOfFunctions()->Add(ex);

%jsroot on
gROOT->GetListOfCanvases()->Draw()